President Barack Obama stepped into the briefing room for a rare press conference with reporters today, riffing on Rep. Todd Akin's (R-Mo.) "legitimate rape" comment, warning Syria on chemical weapons and tweaking Mitt Romney for his refusal to release his tax returns.

Akin's remark has brought some calls from within the GOP for him to withdraw as the Republican nominee running against Sen. Claire McCaskill (D-Mo.).

"The views expressed were offensive," Obama said. "Rape is rape."

The president did not call on Akin to withdraw from the race, but did tie his comment to efforts by Akin and other Republicans in Congress to change the definition of rape.

"We shouldn't have a bunch of politicians, the majority of whom are men, making health care decisions on behalf of women," Obama said.

He also repeatedly jabbed at Romney's campaign tactics while defending his own. Obama dismissed an ad from a super PAC that supports him, Priorities USA, saying that he doesn't hold the presumptive GOP presidential nominee responsible for the cancer death of a woman mentioned in that ad. He said he did not approve the ad and had no control over it, and note that it barely aired on television.

By contrast, Obama contended, Romney is making a "centerpiece of his campaign" a false claim that the president has eliminated work requirements for welfare - a claim that multiple fact-checking groups have labeled false.

"You can't just make stuff up," Obama said. "That's one thing you learn as president of the United States. You get called to account."

Obama said that his campaign has been focused on substantive differences, such as wind energy or tax cuts for the wealthy.

"We don't go out of bounds," Obama said of his campaign. He said that it's not out of bounds to ask for Romney's tax returns.

"I think that is what the American people would rightly expect. ... I think people want to know that everybody's been playing by the same rules, including people who are seeking the highest office in the land. This is not an entitlement, being president of the United States, this is a privilege. We have to put ourselves before the American people to make our case," he said.

Obama also stepped up his rhetoric on Syria, warning that any movement or use of chemical weapons would lead to very serious consequences and change the president's calculus on intervening in that country's conflict.

Obama called the use of chemical weapons "a red line" for the United States.

The White House so far has pushed solely for a political solution in Syria and has rebuffed calls from some in Congress, including Sen. John McCain (R-Ariz.), to arm the rebels, set up no-fly zones and take other military action.